Sensors that can be used to detect a plug chute condition
Plugged chute or blocked chute detection...If
properly implemented, a level sensor / switch or solids flow monitor
can indicate a condition consistent with a flow stoppage within
a chute, hopper or conveying line. Depicted here are some of the
more common methods for plugged chute detection.
A.
Microwave
Solids Flow Detector, model SFD-2 or SFI employed
to monitor the flow or no flow state of the process material.
Benefit:
Non-intrusive monitoring of flow condition.
Caution:
The SFD-2 or SFI cannot differentiate between a plugged no flow condition
and an empty no flow condition.
A logic function must be employed to definitively determine a flow
anomaly. The material flow state is generally compared, either manually
or via computer, against the operating state of the process. If no
flow is detected and the process is in operation, then a problem
can be concluded. If no flow is detected and the process is shut
down, it can then be concluded there is no problem.
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B & C. Point
Level Sensor,
like the SafePoint® and Model KA/KAX Rotary Paddles
or TrueCap® RF
Capacitance Probe, employed to detect the
presence of material that would be exposed to the monitor/sensor
only during a plug condition.
Benefit:
Low cost detection of material backed up in the chute or line; condition
indicative of a flow obstruction.
Caution:
It is problematic to mount a sensing probe directly into a flow stream
to monitor for a plug condition. The level monitor cannot differentiate
between a highly saturated dynamic condition (e.g. dense flow stream)
and a highly saturated static condition (e.g. line plugged). It
is often necessary to make some modification to the process line
so as to isolate the level sensor from the material flow stream.
If the process involves a round pipe it is common to make use of
a pipe Y with the level monitor installed in one leg of the Y. It
is important that the level sensor be installed in such a fashion
so as to ensure that the material clears away from the sensing element
when the plug condition passes.
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D.
Diaphragm-Style
Switch,
like the Model G/GX, is a surface mounted, minimally intrusive pressure
switch that makes it ideal for chutes or vessels limited in size
or internal clearance.
A diaphragm switch provides indication by detecting
pressure applied by the backed-up bulk material to the sensing
diaphragm. The unit should be installed to a chute, line or vessel
wall so that the diaphragm is exposed to the material to be sensed
during a back-up or plugged condition. As material contacts the
diaphragm, a force is exerted through the diaphragm to a pressure
plate within the bin monitor. Physical deflection of the pressure
plate activates an internal switch which is user accessible for
signaling alarms, lights or PLC inputs. When material recedes from
the diaphragm, a light duty spring returns the pressure plate and
internal switch back to their original positions.
Benefit:
Low cost; Minimally intrusive; Fits into area with limited space.
Caution:
Since it is a pressure switch, situations with a lot of air pressure
could cause false alarms. Also, the switch should be placed in
a location where there will only be minimal contact with material,
mainly during a back-up alarm condition. Constant, direct contact
with material flow could cause diaphragm to wear out faster.
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Sensors that can be used to detect a plug chute condition